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Joystick Problems

Symptom: Program does not react correctly on joystick input
         or acts as if joystick is moved, though it is not.
Target : C-64

Possible sources of failure


Joystick ok?

Replace the joystick with a working one. There are two possibilities:
  1. everything works fine -> old joystick defective or
  2. problem does still occur, then goto next step.

CIA #1 or EMI filter(s)?

If possible (i.e. if it is socketed), replace the CIA #1 (the one next to the keyboard connector). For the old boards, this should fix your problems.
If the CIA is not socketed, you should try to determine which of the keybard rows or columns are either continuously active (in this case you usually see one or more characters continuously printed on the screen) or impossible to access by the keyboard routine (in this case some keys of the same row or column are dead). For this test, have a look at the keyboard matrix scheme.

In the new board, you should then unsolder the appropriate EMI filter (next to the control ports) and shortcut it by soldering in a wire between the two outer pins of the three. If this seems to work, you can safely operate your C-64 this way.

In the old board (or if removal of the EMI filter did not help), you could try a pull-up resistor between +5V and the appropriate CIA pin. Try a value of 5.6k. If this works, try 10k too, to minimize the CIA output load, if it does not, try 3.3k.

If nothing of the above helps, your CIA is seriously damaged and must be replaced

Updated: May 18th, 1999
Created: January 1997

Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
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